Photographic developer



Patented Nov. 29, 1938 PHOTOGRAPHIO DEVELOPER Ernst Fournes and HansDiamant-Eerde, Vienna, Austria No Drawing. Application December 20,1935, Serial No. 55,412. In Austria December 31, 1934 8 Claims.

This invention relates to durable photographic developersandfixer-deyelopers for halide-gelatine-silver emulsions containing thelmown organic reducing agents.

In order to simplify operation and to standardize photographicdeveloping of halide-silvergelatine emulsions, standardized chemicalsolutions ready for use are put on the market. This possibility,however, is restricted to certain classes of recipes only, and moreparticularly to those containing alkali carbonate. When caustic alkaliesare used, the durability of the majority of developer solutionscontaining the usual organic reducing agents is very limited. Causticalkali, however, acts as an accelerator, and enables photo-chemicalproblems to be solved, which present insurmountable difficulties as longas alkali carbonate is used. The reason for the poor keeping propertiesof such developers containing caustic alkali is their ready liability toauto-oxidation in the air, that is to say when exposed to theatmosphere.

The present invention is based on the discovery that such developerscontaining caustic alkali can be protected from atmospheric oxidation toa far greater extent than is possible with the usual additions ofsulfite. It is a known fact that carbohydrates, including among othersgrape sugar (dextrose), gain in reducing power when they are treatedwith alkali, this phenomenon being known in 'the Fehling solution. Eulerand collaborators have recently proved that grape sugar solutionscontaining caustic alkali possess in a. high degree the property ofconsuming oxygen from the atmosphere (cf. Zeitschrift fiirphysiologische Chemie., 217, pp. 1 et seq.). At the same time it isprobable that the decomposition of the carbohydrate molecule by thealkali plays an essential part which becomes the more pronounced thehigher the alkalinity of the carbohydrate solution is.

In the alkaline decomposition of carbohydrates there apparently becomeevolved bodies which possess greater reducing power than thecarbohydrates themselves, such as for example methylglyoxalic compounds,glycerine aldehyde, tartronic acid, and the like; from these unstablebodies there can become evolved, by alkaline condensation, still highermolecular products.

We therefore added to developers containing caustic alkali, grape sugarand other carbohydrates such as fruit sugar or cane sugar, in theexpectation that the reducing bodies generated in this way. wouldprotect the developer substance proper from the deleterious action ofthe air.

Furthermore, von

And experience has shown that developer solutions produced in this wayare actually capable of being kept for alonger time than those made upwith sulfite alone.

Sugars, such as grape sugar and its derivatives such as saccharic acid,have it is true been used in the photographic art, but never inconjunctionv with free caustic alkali to produce a particular reducingeifect.

For an example of the use of grape sugar in photography, reference maybe had to Valenta, Photographische Chemie, Austrian Patent No. 16,502,and German Patent No. 185,348, in which mention is made of the use ofthe alkaline salts of saccharic acid. Saccharic acid, however, possessesfar weaker reducing power than sugar solutions containing causticalkali.

With the present invention we have also succeeded in solving a furtherproblem in connection with photographic developing. Present day strivingafter standardization and saving of labor demands the production offixer-developers, that is to say solutions which are capable ofdeveloping and fixing in; a single bath. This result is achieved byadjusting the concentration of the developing and fixing chemicals inthe single solution in such a manner that the developing process sets inrapidly and proceeds at such a rate that it is practically finished bythe time the fixing action starts. The necessarily high velocity of thedeveloping process can be obtained by the addition of caustic alkalies,but at the expense of the durability, that is to say keeping properties,

of the developer. Thus it has not proved possible hitherto to provide asuccessful and durable fixerdeveloper solution, in spite of thepromising reports of various authors (cf. among others Bunel andDesalme, Revue francaise de photographie,

'1921, p. 129; Valenta, Photographische Korrespondenz, 1914, p. 347;Lumiere and Seyewetz, Revue francaise de photographie, 1921, p. 17).

This desirable result can be achieved with fully practical success bythe addition of grape sugar and other carbohydrates of a nature toyield, with

